valve seat recession on LPG
valve seat recession on LPG
(OP)
Hello all,
What is cause valve seat recession on LPG ?
How to reduce this problem?
Thank You!
Radek
What is cause valve seat recession on LPG ?
How to reduce this problem?
Thank You!
Radek





RE: valve seat recession on LPG
2 fit hardened valve seats
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: valve seat recession on LPG
But
this 1. means, wear occurs when the valve is rotated?
or are related to high speed closing the valve at high RPM( valve to seat return)?
+ high temperatures etc.
I mean ,If for example are inappropriate cam lobe design ,clearance or spring preload, that more spring (or other) also may be help?
Radek
RE: valve seat recession on LPG
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: valve seat recession on LPG
I think the consensus was that there is no substitute for hardened valve seats, and no design phase magic bullet that can prevent valve seat recession on gaseous fuel with unhardened seats.
Mike Halloran
Pembroke Pines, FL, USA
RE: valve seat recession on LPG
Radek
RE: valve seat recession on LPG
One of your questions addressed valve rotation. Most of the engine builders who are familiar with gaseous fuels will disable the valve rotators by welding them, or exchanging them with another set of intake spring retainers. The valve tends to rotate slightly during lift and drop. It will tend to drop to the same place without rotators, but with them, the valve will turn slightly. A high speed spectroscopy study will show this process.
Franz
eng-tips, by professional engineers for professional engineers
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RE: valve seat recession on LPG
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: valve seat recession on LPG
Also I wondered if it can be caused(partially) by improper ignition advance,
because I know that more advance = more torque on LPG.
If LPG burning slower, it might způsobit vyšší temperature of the exhaust gases?
Or even burn-in on start phase exhaust(when exhaust open)?
This could also explain the shorter life the catalyst?
I mean that the increased fire advance can help reduce the temperature of exhaust valves.
Radek
RE: valve seat recession on LPG
RE: valve seat recession on LPG
I doubt that engine-out exhaust temperatures are a critical factor for longevity of under-floor catalysts, but I'm willing to be corrected as catalysts are not my area of expertise. I can see where engine-out temperatures could be a hazard to close-coupled catalysts.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: valve seat recession on LPG
LPG equipment used in the rebuilding of modern mpi engines usually can (at least according to correction) to work in the stoichiometric mixture, also uses a partial parallel injection fuel, but does not address the requirement for different ignition timing for gasoline or LPG.
currently may be partially reduce recession only ancillary equipment for dispensing of special additives (eg. Flashlube), but at the expense of many other complications.
I'm trying to understand what may be causing these problems,
because others try to only eliminate its consequences.
Thank you all for your valuable posts
Radek Kolbábek - LPG servis Nedvědice
RE: valve seat recession on LPG
These two factors combine to accelerate exhaust valve recession on engines with exhaust valves that are not specifically engineered for LPG.
The recession phenomenon itself has been described a micro-welding process between the valve and seat, due to the high temperatures and contact pressures; that repeatedly tears away small amounts of material at the zone of contact, resulting in recession.
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: valve seat recession on LPG
RE: valve seat recession on LPG
RE: valve seat recession on LPG
RE: valve seat recession on LPG
RE: valve seat recession on LPG
RE: valve seat recession on LPG
Exhaust valve seat recession is caused by a repeated process of diffusion bonding/welding between the valve and seat contact at closing, that is then followed by the mechanical surface micro welds being torn apart when the valve is opened. The result is that a tiny amount of material is transferred from the seat face to the valve face during each cycle. The TEL added to leaded gasoline inhibited the diffusion bonding process between the exhaust valve face and the seat by forming an inert oxide coating on the contact surfaces.
The higher gas pressure force acting on the exhaust valve face from pre-ignition conditions would not result in any appreciable increase in contact stress levels at the exhaust valve/seat contact.
RE: valve seat recession on LPG
very interesting!!!
Radek